April 8, 2011 -- Please note: Some jerk has spray-painted over the first couple of signs at the bottom of the walkway, but that shouldn't affect your ability to collect all the information you need to answer these questions.
To log this EarthCache, you'll need to answer a few questions. All the information you'll need can be found on signs posted along the roughly quarter-mile walk along this road cut from the parking lot to the end of the path. It's a very gentle climb, and a the path is usually in good shape, but there can be mud from small landslides, so watch your footing, especially after rain or snow.
Interstate 70 cuts through the Dakota Hogback west of Denver near Morrison and provides an excellent view into Colorado’s geological past. On both sides of the highway, there are parking lots and easy footpaths along the road cut. This EarthCache focuses on information found on interpretive signs along the northern road cut.
The cut, made during interstate construction in 1971, exposes rocks from the Morrison Formation and Dakota Group. These rocks were laid down in the Upper Jurassic and Cretaceous periods, or from about 160 million years ago to about 65 million years ago. The land here and along much of the eastern fringe of the Rocky Mountains was thrust upward between 80 million years ago and 50 million years ago during an event called the Laramide orogeny, which was responsible for raising the Rocky Mountains.
Posting a photo taken from the site is no longer allowed as a logging requirement, but it would be great to see some pictures besides the not-so-great one I’ve posted here.
Please go ahead and log your find, and as soon afterward as you can, send me answers to the following questions in an e-mail (send it through my profile link at the top of this page). Oh, and don’t forget to find the nearby multicache!
1. What caused the variations in color of the rocks, and what kinds of minerals were affected to make the colors?
2. What do the light and dark laminations in the clay bed indicate?
3. What caused the black color of the rocks about halfway up the walk?
4. Why can you use your sense of smell to know you’re in the right place at a certain point along the walk?
5. How thick are the various layers of rock here, and how many years did it take for each layer to build up?
http://www.cliffshade.com/colorado/dakota_hogback/#i-70 (With permission, Colorado Geology Photojournal, a personal web site authored by Jeremy McCreary, Research Associate, Colorado School of Mines, Golden, CO)